ACK/NACK signal processing method and device for uplink multi-user transmission

ABSTRACT

The present document relates to a method and device for an Access Point (AP) to transmit ACK/NACK signals for MU (Multi-User) transmission data of a plurality of stations (STA) in a wireless LAN (WLAN) system. To this end, the method and device are characterized in that a STA responds to a trigger frame received from an AP, transmits data to the AP through an MU access technique, and sets an ACK policy value for data transmitted on the basis of the trigger frame to another value other than a first ACK policy value requesting an ACK signal transmission on the basis of a block ACK request.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2016/011204, filed on Oct. 6, 2016,which claims the benefit of U.S. Provisional Application No. 62/238,146,filed on Oct. 7, 2015, the contents of which are all hereby incorporatedby reference herein in their entirety.

TECHNICAL FIELD

The present disclosure relates to a method and apparatus fortransmitting and receiving an Acknowledgment/Negative Acknowledgment(ACK/NACK) signal for multi-user or multi-Station (STA) data, based onan ACK policy value in a Wireless Local Area Network (WLAN) system.

BACKGROUND ART

WLAN technology has been standardized as Institute of Electrical andElectronics Engineers (IEEE) 802.11. IEEE 802.11a and IEEE 802.11b usean unlicensed band at 2.4 GHz or 5 GHz. IEEE 802.11b provides atransmission rate of 11 Mbps, and IEEE 802.11a provides a transmissionrate of 54 Mbps. IEEE 802.11g provides a transmission rate of 54 Mbps byapplying Orthogonal Frequency Division Multiplexing (OFDM) at 2.4 GHz.IEEE 802.11n provides a transmission rate of 300 Mbps for four spatialstreams by applying Multiple Input Multiple Output (MIMO)-OFDM. IEEE802.11n supports a channel bandwidth of up to 40 MHz and, in this case,provides a transmission rate of 600 Mbps.

The above-described WLAN standards have evolved into IEEE 802.11ac thatuses a bandwidth of up to 160 MHz and supports a transmission rate of upto 1 Gbit/s for eight spatial streams, and IEEE 802.11ax standardizationis under discussion.

DISCLOSURE Technical Problem

In the IEEE 802.11ax standard, Uplink (UL) Orthogonal Frequency DivisionMultiple Access (OFDMA) transmission and UL Multi-User (MU) transmissionwill be used. Thus, an Access Point (AP) may receive UL MU frames from aplurality of Stations (STAs) in the same transmission opportunity andneeds to transmit an Acknowledgement (ACK) frame in response to the ULMU frames.

In this case, efficient transmission of Acknowledgement/NegativeAcknowledgement (ACK/NACK) signals to a plurality of STAs in a Block ACK(BA) frame may be considered. However, overhead may be problematic dueto an increased size of an MU BA or M-BA frame for the plurality ofSTAs.

Moreover, if some of the plurality of STAs request a BA and othersrequest a normal ACK, the procedure becomes complex and an ACK/NACKoperation may be delayed.

Hereinafter, a method and apparatus for efficiently transmitting anACK/NACK signal in the above-described UL MU transmission situation willbe described.

Technical Solution

In an aspect of the present disclosure, a method for accessing an accesspoint (AP) in a multi-user scheme by a station (STA) in a wireless localarea network (WLAN) system includes receiving a trigger frame from theAP, and transmitting data to the AP in a multi-user access scheme inresponse to the trigger frame. The STA sets an ACK policy value for thedata transmitted based on the trigger frame to a value other than afirst ACK policy value requesting transmission of an ACK signal based ona block ACK request.

The STA may set the ACK policy value for the data transmitted based onthe trigger frame to a second ACK policy value requesting a normal ACKor an immediate transmission block ACK request.

The method may further include, after transmission of the data with theACK policy value set to the second ACK policy value, receiving anACK/NACK signal for the data from the AP.

The ACK/NACK signal may be received a short inter-frame space (SIFS)after the transmission of the data with the ACK policy value set to thesecond ACK policy value.

If downlink data is received in a multi-user scheme from the AP, an ACKpolicy value for the downlink data may be set to one of a plurality ofACK policy values including the first ACK policy value.

The plurality of ACK policy values may include ‘01’ requesting a normalACK or an immediate transmission block ACK request, ‘01’ requesting noACK, ‘10’ requesting no explicit ACK or a power save multi-poll (PSMP)ACK, and ‘11’ requesting an ACK based on a block ACK request.

The first ACK policy value may be ‘11’, and the second ACK policy valuemay be ‘00’.

In another aspect of the present disclosure, a STA for accessing an APin a multi-user scheme in a WLAN system includes a transceiverconfigured to receive a trigger frame from the AP, and transmit data tothe AP in a multi-user access scheme in response to the trigger frame,and a processor connected to the transceiver and configured to providethe data to the transceiver. The processor is configured to set an ACKpolicy value for the data transmitted based on the trigger frame to avalue other than a first ACK policy value requesting transmission of anACK signal based on a block ACK request.

The processor may be configured to set the ACK policy value for the datatransmitted based on the trigger frame to a second ACK policy valuerequesting a normal ACK or an immediate transmission block ACK request.

If the transceiver receives downlink data in a multi-user scheme fromthe AP, the processor may be configured to check an ACK policy value forthe downlink data set to one of a plurality of ACK policy valuesincluding the first ACK policy value.

In another aspect of the present disclosure, a method for receiving datafrom a plurality of STAs in a multi-user scheme by an AP in a WLANsystem includes transmitting a trigger frame to the plurality of STAs,and receiving data from the plurality of STAs in a multi-user accessscheme. An ACK policy value for the data received after the transmissionof the trigger frame is set to a value other than a first ACK policyvalue requesting transmission of an ACK signal based on a block ACKrequest.

The ACK policy value for the data received after the transmission of thetrigger frame may be set to a second ACK policy value requesting anormal ACK or an immediate transmission block ACK request.

If the AP transmits downlink data to the plurality of STAs in amulti-user scheme, the AP may set an ACK policy value for the downlinkdata to one of a plurality of ACK policy values including the first ACKpolicy value.

In another aspect of the present disclosure, an AP for receiving datafrom a plurality of STAs in a multi-user scheme in a WLAN systemincludes a transceiver configured to transmit a trigger frame to theplurality of STAs, and receive data from the plurality of STAs in amulti-user access scheme, and a processor connected to the transceiverand configured to process the data. The processor is configured tooperate in response to an ACK policy value for the data set to a valueother than a first ACK policy value requesting transmission of an ACKsignal based on a block ACK request.

The ACK policy value for the data received after the transmission of thetrigger frame may be set to a second ACK policy value requesting anormal ACK or an immediate transmission block ACK request.

Advantageous Effects

According to the present disclosure as described above, an Access Point(AP) may efficiently transmit Acknowledgment/Negative Acknowledgment(ACK/NACK) signals to a plurality of Stations (STAs) in an Uplink (UL)Multi-User (MU) transmission situation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating an exemplary configuration of a WirelessLocal Area Network (WLAN) system.

FIG. 2 is a view illustrating another exemplary configuration of a WLANsystem.

FIG. 3 is a view illustrating a Block Acknowledgment (ACK) mechanismused in a WLAN system.

FIG. 4 is a view illustrating a basic configuration of a Block ACKframe.

FIG. 5 is a view illustrating a detailed configuration of a BA Controlfield illustrated in FIG. 4.

FIG. 6 is a view illustrating a detailed configuration of a Block ACK(BA) Information field illustrated in FIG. 4.

FIG. 7 is a view illustrating a configuration of a Block Ack StartingSequence Control subfield.

FIG. 8 is a view illustrating a configuration of a BA Information fieldof a compressed Block ACK frame.

FIG. 9 is a view illustrating a BA Information field of a Multi-TrafficIdentifier (TID) Block ACK frame.

FIGS. 10 and 11 are views illustrating cases in which a Block ACKmechanism is applied to Downlink (DL) Multi-User Multiple Input MultipleOutput (MU-MIMO).

FIG. 12 is a view illustrating an Uplink (UL) MU transmission situationto which the present disclosure is applied.

FIG. 13 is a view illustrating a method for transmitting ACK/NACKsignals to a plurality of STAs, using an ACK policy according to anembodiment of the present disclosure.

FIG. 14 is a view illustrating a case in which a Block ACK Request(BAR)-based ACK policy value is not used according to an embodiment ofthe present disclosure.

FIGS. 15 and 16 are views additionally illustrating a UL multiple accesssituation to which the present disclosure is applied.

FIGS. 17 and 18 are views illustrating ACK policy values in a triggerframe transmitted by an Access Point (AP).

FIG. 19 is a block diagram of apparatuses for implementing the abovemethods.

BEST MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to the exemplary embodiments of thepresent disclosure, examples of which are illustrated in theaccompanying drawings. The detailed description, which will be givenbelow with reference to the accompanying drawings, is intended toexplain exemplary embodiments of the present disclosure, rather than toshow the only embodiments that can be implemented according to thepresent disclosure.

The following detailed description includes specific details in order toprovide a thorough understanding of the present disclosure. However, itwill be apparent to those skilled in the art that the present disclosuremay be practiced without such specific details. In some instances, knownstructures and devices are omitted or are shown in block diagram form,focusing on important features of the structures and devices, so as notto obscure the concept of the present disclosure.

As described above, the following description relates to a method forefficiently utilizing a channel having a wide band in a Wireless LocalArea Network (WLAN) system and an apparatus therefor. To this end, aWLAN system to which the present disclosure is applicable will first bedescribed in detail.

FIG. 1 is a view illustrating an exemplary configuration of a WLANsystem.

As illustrated in FIG. 1, the WLAN system includes at least one BasicService Set (BSS). A BSS is a set of Stations (STAs) that are able tocommunicate with each other by successful synchronization.

A STA is a logical entity including a physical layer interface between aMedia Access Control (MAC) layer and a wireless medium. The STA may beany of an Access Point (AP) and a non-AP STA. Among STAs, a portableterminal manipulated by a user is a non-AP STA. If a terminal is simplycalled a STA, the STA refers to a non-AP STA. The non-AP STA may also bereferred to as a terminal, a Wireless Transmit/Receive Unit (WTRU), aUser Equipment (UE), a Mobile Station (MS), a mobile terminal, or amobile subscriber unit.

An AP is an entity that provides access to a Distribution System (DS) toa STA associated with the AP through a wireless medium. The AP may alsobe referred to as a centralized controller, a Base Station (BS), aNode-B, a Base Transceiver System (BTS), or a site controller.

BSSs may be classified into infrastructure BSS and Independent BSS(IBSS).

The BSSs illustrated in FIG. 1 are IBSSs. An IBSS refers to a BSS thatdoes not include an AP. Since the IBSS does not include an AP, the IBSSis not allowed to access to the DS and thus forms a self-containednetwork.

FIG. 2 is a diagram illustrating another exemplary configuration of aWLAN system.

BSSs illustrated in FIG. 2 are infrastructure BSSs. Each infrastructureBSS includes one or more STAs and one or more APs. In the infrastructureBSS, communication between non-AP STAs is basically conducted via an AP.However, if a direct link is established between the non-AP STAs, directcommunication is also possible between the non-AP STAs.

As illustrated in FIG. 2, a plurality of infrastructure BSSs may beinterconnected via a DS. The BSSs interconnected via the DS are calledan Extended Service Set (ESS). STAs included in the ESS may communicatewith each other, and a non-AP STA within the same ESS may move from oneBSS to another BSS while seamlessly performing communication.

The DS is a mechanism that connects a plurality of APs to one another.The DS is not necessarily a network. As long as it provides a specificdistribution service, the DS is not limited to any specific form. Forexample, the DS may be a wireless network such as a mesh network or maybe a physical structure that connects APs to one another.

Now, a description will be given of a Block ACK mechanism in a WLANsystem based on the above description.

The Block ACK mechanism is a scheme of transmitting a plurality ofACK/NACK signals in one frame, thereby increasing channel efficiency.For the Block ACK mechanism, two response schemes are available:immediate response and delayed response. The immediate response schememay be favorable for transmission of traffic with a short latency in awide bandwidth, whereas the delayed response scheme may be suitable fora delay-tolerant application. Unless otherwise specified in thefollowing description, a STA transmitting data in the Block ACKmechanism is referred to as an originator, and a STA receiving the datais referred to as a recipient.

FIG. 3 is a view illustrating a Block ACK mechanism in a WLAN system.

As illustrated in FIG. 3, the Block ACK mechanism may be initiated byexchange between an Add Block Acknowledgement (ADDBA) request frame andan ADDBA response frame ((a) Setup). After the Block ACK mechanism isinitiated in this manner, an originator may transmit Quality of Service(QoS) data frame blocks to a recipient. As the originator wins a polledTransmit Opportunity (TXOP) or an Enhanced Distributed Channel Access(EDCA) contention, transmission of these blocks may be started. Thenumber of frames in a block may be limited. Reception or non-receptionof MAC Protocol Data Units (MPDUs) included in such a frame block may beconfirmed from a Block ACK frame received in response to a request madeby a BlockAckReq frame ((b)) Data & Block ACK).

If the originator does not have any more transmission data and a finalBlock ACK exchange is completed, the originator may end the Block ACKmechanism by transmitting a Delete Block Acknowledgement (DELBA) frameto the recipient. Upon receipt of the DELBA frame, the recipient mayrelease all resources allocated for Block ACK transmission ((c) TearDown).

FIG. 4 is a view illustrating a basic configuration of a Block ACK (BA)frame.

As illustrated in FIG. 4, the BA frame may include a MAC Header field, aBA Control field, and a BA Information field. The MAC Header field mayinclude a Frame Control field, a Duration/ID field, an RA field, and aTA field. Herein, the RA field represents an address of a receiving STAand the TA field represents an address of an originating STA.

FIG. 5 is a view illustrating a detailed configuration of the BA Controlfield illustrated in FIG. 4.

The values of a BA Ack Policy subfield in the BA Control field may havethe meanings described in [Table 1] below.

TABLE 1 Value Meaning 0 Normal Acknowledgment The BA Ack Policy subfieldis set to this value when the sender requires immediate acknowledgment.The addressee returns an Ack frame. The value 0 is not used for datasent under HT-delayed Block Ack during a PSMP sequence. The value 0 isnot used in frames transmitted by DMG STAs. 1 No Acknowledgment. Theaddressee sends no immediate response upon receipt of the frame. The BAAck Policy is set to this value when the sender does not requireimmediate acknowledgment. The value 1 is not used in a Basic BlockAckframe outside a PSMP sequence. The value 1 is not used in an Multi-TIDBlockAck frame.

Meanwhile, Multi-Traffic Identifier (Multi-TID), Compressed Bitmap, andGCR subfields in the BA Control field may determine possible BlockAckframe variants according to the following regulation.

TABLE 2 Compressed Multi-TID Bitmap GCR BlockAck subfield value subfieldvalue subfield value frame variant 0 0 0 Basic BlockAck 0 1 0 CompressedBlockAck 1 0 0 Extended Compressed BlockAck 1 1 0 Multi-TID BlockAck 0 01 Reserved 0 1 1 GCR BlockAck 1 0 1 Reserved 1 1 1 Reserved

FIG. 6 is a view illustrating a detailed configuration of the BAInformation field illustrated in FIG. 4, and FIG. 7 is a viewillustrating a configuration of a Block Ack Starting Sequence Controlsubfield.

As illustrated in FIG. 6, the BA Information field may include a BlockAck Starting Sequence Control (SSC) subfield and a Block Ack Bitmapsubfield.

As illustrated in FIG. 6, the Block Ack Bitmap subfield is 128 octets inlength, and thus may represent the reception statuses of 64 MAC ServiceData Units (MSDUs). If bit position n in the Block Ack Bitmap subfieldis set to 1, this may indicate that an MPDU having an MPDU sequencecontrol value corresponding to (SSC+n) has been successfully received.Herein, SSC represents the value of the Block Ack Starting SequenceControl subfield. On the other hand, if bit position n of the Block AckBitmap field is set to 0, this may indicate that the MPDU having theMPDU sequence control value corresponding to (SSC+n) has not beenreceived. Each of the values of an MPDU Sequence Control field and theBlock Ack Starting Sequence Control subfield may be treated as a 16-bitunsigned integer. For unused fragment numbers of an MSDU, correspondingbits in the bitmap may be set to 0.

FIG. 8 is a view illustrating a configuration of a BA Information fieldin a compressed Block ACK frame.

As illustrated in FIG. 8, a Block Ack Bitmap subfield of the BAInformation field of the compressed Block ACK frame may be 8 octets inlength and indicate the reception statuses of 64 MSDUs and AggregateMSDUs (A-MSDUs). The first bit of the bitmap corresponds to an MSDU orA-MSDU matching a value of a Block Ack Starting Sequence Controlsubfield, and each bit of the bitmap may sequentially correspond to anMSDU or A-MSDU following the above MSDU or A-MSDU.

FIG. 9 is a view illustrating a BA Information field in a Multi-TIDBlock ACK frame.

A TID_INFO subfield of a BA Information field in the Multi-TID Block ACKframe contains information about the number of TIDs in the BAInformation field. Specifically, a value of the TID_INFO subfieldrepresents (the number of TIDs corresponding to information of the BAInformation field)−1. For example, if the value of the TID_INFO subfieldis 2, this may indicate that the BA Information field containsinformation about three TIDs.

Meanwhile, the Multi-TID Block ACK frame may include a Per TID Infosubfield in addition to a Block Ack Starting Sequence Control subfieldand a Block Ack Bitmap subfield as illustrated in FIG. 9. The first PerTID Info, Block Ack Starting Sequence Control, and Block Ack Bitmapsubfields may be transmitted in correspondence to a lowest TID value,and subsequent repeated subfields may correspond to the next TID. Atriplet of these subfields may be repeated per TID.

FIGS. 10 and 11 are views illustrating cases in which the Block ACKmechanism is applied to DL MU-MIMO.

As illustrated in FIGS. 10 and 11, an AP may transmit an MU-MIMO dataframe to a plurality of STAs (STA1, STA2, and STA3).

In FIG. 10, it is assumed that frames are exchanged a Short Inter-FrameSpace (SIFS) after transmission of a Multi-User PLCP Protocol Data Unit(MU PPDU). It is assumed in FIG. 10 that Implicit Block ACK Request isset as an ACK policy for STA1, and Block ACK is set as an ACK policy forSTA2 and STA3. Therefore, STA1 may receive a BA frame immediately afterreceiving the DL MU PPDU without a BA request. On the other hand, the APmay perform polling for STA2 and STA3 by transmitting BA Request (BAR)frames to STA2 and STA3. STA2 and STA3 may transmit BA frames inresponse to the BAR frames.

Meanwhile, FIG. 11 illustrates an example in which frames are exchangedwithout an SIFS after transmission of an MU PPDU. It is assumed in FIG.11 that Block ACK is set as an ACK policy for all STAs. Therefore, theAP may perform polling by transmitting a BAR frame to every STA.

FIG. 12 is a view illustrating a UL MU transmission situation to whichthe present disclosure is applied.

As described above, UL MU transmission may be used in the 802.11axsystem. As illustrated in FIG. 12, as an AP transmits a trigger frame toa plurality of STAs (e.g., STA1 to STA4), UL MU transmission may bestarted. The trigger frame may include UL MU allocation information(e.g., resource positions and sizes, STA IDs, a Modulation and CodingScheme (MCS), an MU type (MIMO, OFDMA, or the like)). Specifically, forexample, the following information may be transmitted in the triggerframe.

TABLE 3 Duration, Number of allocations (N), each allocation'sinformation, and SU/MU AID (as many as the number of STAs in the case ofMU). Power adjustment, Tone(/Resource) allocation information (e.g.,bitmap), MCS, Nsts, STBC, Coding, Beamformed, etc.

Meanwhile, as illustrated in FIG. 12, the AP may acquire a TXOP in whichto transmit a trigger frame by contention for medium access. Then, theSTAs may transmit UL data frames in a format indicated by the AP, anSIFS after the trigger frame. In the present disclosure, it is assumedthat the AP performs an ACK/NACK procedure for the UL MU data frames bya Block ACK (BA) frame.

In UL multiple access, flexible application of an ACK policy value perSTA may be considered in order to render an ACK/NACK signal transmissionscheme of an AP to be flexible.

A QoS Control field of a UL MU frame has the following configuration.Particularly, the QoS Control field has a 2-bit field indicating an ACKpolicy in bits 5 and 6.

TABLE 4 Applicable frame (sub) types Bits 0-3 Bit 4 Bits 5-6 Bit 7 Bits8 Bit 9 Bit 10 Bits 11-15 Qos CF-Poll and QoS CF- TID EOSP Ack ReservedTXOP Limit Ack + CF-Poll frames sent Policy by HC QoS Data + CF-Poll andTID EOSP Ack A- TXOP Limit QoS data + CF-Ack + CF- Policy MSDU PollFrames sent by HC Present QoS Data and QoS TID EOSP Ack A- AP PS BufferState Data + CF-Ack frames sent Policy MSDU by HC Present QoS Nullframes sent by TID EOSP Ack Reserved AP PS Buffer State HC Policy QoSData and QoS TID 0 Ack A- TXOP Duration Requested Data + CF-Ack framessent Policy MSDU by non-AP STAs that are Present not a TPU buffer STA ora TID 1 Ack A- Queue Size TPU sleep STA in a Policy MSDU nonmesh BSSPresent QoS Null frames sent by TID 0 Ack Reserved TXOP DurationRequested non-AP STAs that are not a Policy TPU buffer STA or a TPU TID1 Ack Reserved Queue Size sleep STA in a nonmesh Policy BSS

TABLE 5 Applicable frame (sub) types Bits 0-3 Bit 4 Bits 5-6 Bit 7 Bits8 Bit 9 Bit 10 Bits 11-15 QoS Data and QoS TID EOSP Ack A- ReservedData + CF-Ack frames sent Policy MSDU by TPU buffer STAs in a Presentnonmesh BSS QoS Null frames sent by TID EOSP Ack Reserved Reserved TPUbuffer STAs in a Policy nonmesh BSS QoS Data and QoS TID Reserved Ack A-Reserved Data + CF-Ack frames sent Policy MSDU by TPU sleep STAs in aPresent nonmesh BSS QoS Null frames sent by TID Reserved Ack ReservedReserved TPU sleep STAs in a Policy nonmesh BSS All frames sent by meshTID EOSP Ack A- Mesh Mesh RSPI Reserved STAs in a mesh BSS Policy MSDUControl Power Present Present Save Level

The values of the Ack Policy field illustrated in [Table 4] and [Table5] are set as follows.

TABLE 6 Ack Policy ==00 Normal Ack or Implicit Block Ack Request. In aframe that is a non-A-MPDU frame or VHT single MPDU: The addressedrecipient returns an Ack or QoS +CF-Ack frame after a short interframespace (SIFS) period, according to the procedures defined in Ackprocedure and HCCA transfer rules. A non-DMG STA sets the Ack Policysubfield for individually addressed QoS Null (no data) frames to thisvalue. Otherwise: The addressed recipient returns a BlockAck frame,either individually or as part of an A- MPDU starting a SIFS after thePPDU carrying the frame, according to the procedures defined in Blockack procedure, Generation and transmission of BlockAck frames by an HTSTA or DMG STA, Operation of HT-delayed block ack, Rules for RDinitiator, Rules for RD responder, and Explicit feedback beamforming.

TABLE 7 Ack Policy ==10 No Ack The addressed recipient takes no actionupon receipt of the frame. The Ack Policy subfield is set to this valuein all individually addressed frames in which the sender does notrequire acknowledgment. The Ack Policy subfield is also set to thisvalue in all group addressed frames that use the QoS frame format exceptwith a TID for which a block ack agreement exists. This value of the AckPolicy subfield is not used for QoS Data frames with a TID for which ablock ack agreement exists. The Ack Policy subfield for group addressedQoS Null (no data) frames is set to this value.

TABLE 8 Ack Policy ==01 No explicit acknowledgment or PSMP Ack or MUAck. When bit 6 of the Frame Control field (see 9.2.4.1.3 (Type andSubtype subfields)) is set to 1: There might be a response frame to theframe that is received, but it is neither the Ack frame nor any Dataframe of subtype +CF-Ack. The Ack Policy subfield for QoS CF-Poll andQoS CF-Ack +CF-Poll Data frames is set to this value. When bit 6 of theFrame Control field (see 9.2.4.1.3 (Type and Subtype subfields)) is setto 0: The acknowledgment for a frame indicating PSMP Ack when it appearsin a PSMP downlink transmission time (PSMP-DTT) is to be received in alater PSMP uplink transmission time (PSMP-UTT). The acknowledgment for aframe indicating PSMP Ack when it appears in a PSMPUTT is to be receivedin a later PSMP-DTT. For a frame that is carried in a DL HE MU PPDU: TheAck Policy subfield for the frame that solicits an immediate response ina HE Trigger- based PPDU is set to this value (MU Ack). The addressedrecipient returns an Ack, BlockAck, or Multi-STA BlockAck frame in theHE trigger-based PPDU format after a SIFS period, according to theprocedures defined in 10.3.2.11.2 (Acknowledgement procedure for HE MUPPDU in MU format) and 25.5.2 (UL MU operation). (#2445) NOTE - Bit 6 ofthe Frame Control field (see 9.2.4.1.3 (Type and Subtype subfields))indicates the absence of a data Frame Body field. When equal to 1, theQoS Data frame contains no Frame Body field, and any response isgenerated in response to a QoS CF-Poll or QoS CF-Ack +CF-Poll frame, butdoes not signify an acknowledgment of data. When set to 0, the QoS Dataframe contains a Frame Body field, which is acknowledged as described in10.29.2.7 (PSMP acknowledgment rules).

TABLE 9 Ack Policy ==11 Block Ack The addressed recipient takes noaction upon the receipt of the frame except for recording the state. Therecipient can expect a BlockAckReq frame in the future to which itresponds using the procedure described in Block acknowledgment (blockack).

That is, the above-described Ack Policy field may represent fourdifferent values by 2-bit information, and each of the values of the AckPolicy field is defined in [Table 6] to [Table 9]. In the followingdescription, a method for transmitting ACK/NACK signals to a pluralityof STAs more flexibly by an AP through application of the Ack Policyfield to a UL MU situation. ACK policy values used in the followingdescription may have additional meanings as set forth below in additionto the meanings described in [Table 6] to [Table 9]. However, unlessotherwise specified, it is assumed that the ACK policy values arepursuant to the definitions in [Table 6] to [Table 9].

FIG. 13 is a view illustrating a method for transmitting ACK/NACKsignals to a plurality of STAs, using an ACK policy according to anembodiment of the present disclosure.

As in the example of FIG. 13, the AP may trigger transmission of UL MUframes by transmitting a trigger frame to STA1 to STA4. Accordingly,when transmitting the UL MU frames, STA1 to STA4 may include AckPolicies in MPDUs. In FIG. 13, it is assume that STA1 and STA3 set AckPolicy values to 00 and STA2 and STA4 set Ack Policy values to 11.

It is assumed in this embodiment that if the Ack Policy value of a UL MUframe is 00, this indicates an implicit BA/ACK request for a singleMPDU, and the AP may simultaneously transmit a BA (i.e., an M-BA) toSTAs that have transmitted UL MU frames with Ack Policy==00 (implicitBA/ACK), immediately an SIFS after receiving the UL MU frames from theSTAs. The M-BA is assumed to include ACKs/BAs for the plurality of STAs.That is, upon receipt of one or more UL MU frames with Ack Policy==00,the AP transmits an M-BA an SIFS later. Then, after receiving BARs fromSTAs that have transmitted UL MU frames with Ack Policy set to 11indicating BA, the AP may transmit a Block ACK to the STAs that havetransmitted the BARs.

In FIG. 13, since Ack Policies of STA1 and STA3 are 00 (implicit BA orACK for single MPDU), the AP transmits a BAs/ACKs (i.e., an M-BA) toSTA1 and STA3 at one time, an SIFS after reception of UL MU frames.Herein, the AP may transmit a Block ACK (multi-STA BA) including BA/ACKinformation for multiple STAs.

Subsequently, the AP may await receipt of BARs from STA2 and STA4 thathave transmitted UL frames with Ack Policy set to 11 indicating BA.Then, STA2 may transmit a BAR in a contention-based manner, and the APmay transmit a BA to STA2 in response to the BAR. Subsequently, STA4 maytransmit a BAR in a contention-based manner, and the AP may transmit aBA to STA4 in response to the BAR.

However, if ACK policy values are flexibly used for each of a pluralityof STAs as in FIG. 13, the UL MU operation may become complex.Particularly when a STA uses Ack Policy set to ‘11’, the AP shouldtransmit an ACK after awaiting receipt of a BAR from the STA, theprocedure may be delayed.

Accordingly, a preferred embodiment of the present disclosure proposesthat an ACK policy value of ‘11’ is not used in a UL MU situation. Thus,it is assumed that a STA transmits data in UL MU and sets an ACK policyvalue to a value other than ‘11’ (e.g., ‘00’, ‘01’, or ‘10’). Therefore,when requesting an ACK/NACK, the STA preferably operates by setting AckPolicy to ‘00’.

The above UL MU situation may be different from the afore-described DLMU situation. In DL MU, since an AP may uniformly determine ACK policyvalues for a plurality of STAs, the AP may select a BAR-based ACK policyfor some STA according to the situation of the AP.

FIG. 14 is a view illustrating a case in which a BAR-based ACK policyvalue is not used according to an embodiment of the present disclosure.

As described in FIG. 14, an AP may trigger transmission of UL MU framesfrom a plurality of STAs by transmitting a trigger frame. Thus, it isassumed that each of STA1 to STA4 transmits a UL MU frame, requestingreception of an ACK/NACK for the UL MU frame in the example of FIG. 14.Accordingly, STA1 to STA4 transmit UL MU frames with Ack Policy set to‘00’, and thus receive ACK/NACK signals after an SIFS from the AP.

Meanwhile, the AP is shown in FIG. 14 as transmitting ACK/NACK signalsin an M-BA, by way of example. Thus, the AP may transmit all of ACK/NACKsignals for STA1 to STA4 in the M-BA.

FIGS. 15 and 16 are views additionally illustrating a UL multiple accesssituation to which the present disclosure is applied.

FIG. 15 is a view illustrating a situation in which STA1 to STA4transmit UL MU PPDUs in response to a trigger frame transmitted by anAP, as described above. In FIG. 15, since STA1, STA2, and STA3 requestACK/NACK signals for their transmitted UL MU PPDUs, STA1, STA2, and STA3preferably transmit the UL MU PPDUs with Ack Policy set to ‘00’. Incontrast, STA4 does not request an ACK/NACK signal for its transmittedUL MU PPDU, and thus may transmit the UL MU PPDU with Ack Policy set to‘01’.

Therefore, the AP may transmit ACK/NACK signals in a DL OFDMA BA or M-BAto STA1, STA2, and STA3 that have set Ack Policy to ‘00’.

Meanwhile, as illustrated in FIG. 16, the AP may transmit a DL MU PPDUtogether with a trigger frame. Thus, after the STAs transmit UL MU PPDUsor UL ACKs, the AP may transmit a DL ACK for a UL MU PPDU for which anACK is needed. Herein, trigger information for transmission of an ACKfor a DL MU PPDU may be included or may be implicitly derived.

A DL ACK frame may be transmitted in an OFDMA or M-BA form. That is,each piece of ACK information transmitted to each STA may be configuredin an OFDMA frame or ACK information transmitted to all STAs may beaggregated in one frame. A hybrid scheme of the two schemes is alsopossible, in which an M-BA is used only within 20 MHz, and OFDMA is usedin a bandwidth equal to or larger than 20 MHz.

If compared to a DL MU situation, different ACK policy values are setfor different STAs in a UL MU situation as described above, theprocedure may become complex and an unnecessary delay may occur.Therefore, it is preferred not to use an ACK policy value of ‘11’.

However, to solve the problem of selecting a different ACK policy valuefor each STA in a UL MU situation as described above and flexibly use anACK policy according to the state of each STA, another embodiment of thepresent disclosure proposes that an AP sets a per-STA ACK policy by atrigger frame.

FIGS. 17 and 18 are views illustrating ACK policy values in a triggerframe transmitted by an AP.

The AP may set the same or different ACK policies for all STAs in atrigger frame. FIG. 17 illustrates an example of setting the same AckPolicy==00 (implicit BA) for all STAs, and FIG. 18 illustrates anexample of setting an ACK Policy on a STA basis.

In the example of FIG. 18, Ack Policy (A_P) is set to 00 (implicitBA/ACK for single MPDU) for STA1 and STA3, and A_P is set to 11 (BlockACK) for STA2 and STA4. Therefore, the AP may receive UL MU frames,transmit BAs/ACKs for STA1 and STA3 in an M-BA, and then allocateresources for MU BAR transmission to STA2 and STA4 by a trigger frame.

FIG. 19 is a block diagram of apparatuses for implementing theabove-described methods.

A wireless apparatus 800 of FIG. 19 may correspond to theabove-described specific STA, and a wireless apparatus 850 of FIG. 19may correspond to the above-described AP.

The STA 800 may include a processor 810, a memory 820, and a transceiver830, and the AP 850 may include a processor 860, a memory 870, and atransceiver 880. The transceivers 830 and 880 may transmit/receive awireless signal and may be implemented in a physical layer of IEEE802.11/3GPP. The processors 810 and 860 are implemented in a physicallayer and/or a MAC layer and are connected to the transceivers 830 and880. The processors 810 and 860 may perform the above-described UL MUscheduling procedure.

The processors 810 and 860 and/or the transceivers 830 and 880 mayinclude an Application-Specific Integrated Circuit (ASIC), otherchipsets, a logical circuit, and/or a data processor. The memories 820and 870 may include a Read-Only Memory (ROM), a Random Access Memory(RAM), a flash memory, a memory card, a storage medium, and/or a storageunit. If an embodiment is performed by software, the above-describedmethods may be executed in the form of a module (e.g., a process or afunction) performing the above-described functions. The module may bestored in the memories 820 and 870 and executed by the processors 810and 860. The memories 820 and 870 may be located at the interior orexterior of the processors 810 and 860 and may be connected to theprocessors 810 and 860 via known means.

The detailed description of the preferred embodiments of the presentdisclosure has been given to enable those skilled in the art toimplement and practice the present disclosure. Although the presentdisclosure has been described with reference to the preferredembodiments, those skilled in the art will appreciate that variousmodifications and variations can be made in the present disclosurewithout departing from the spirit or scope of the present disclosuredescribed in the appended claims. Accordingly, the present disclosureshould not be limited to the specific embodiments described herein, butshould be accorded the broadest scope consistent with the principles andnovel features disclosed herein.

INDUSTRIAL APPLICABILITY

While the present disclosure has been described in the context of anIEEE 802.11 WLAN system, the present disclosure is not limited thereto.The present disclosure is applicable in the same manner to variouswireless systems in which an AP is capable of performing a Block ACKmechanism for a plurality of STAs.

What is claimed is:
 1. A method for accessing an access point (AP) in anuplink multi-user transmission scheme by a station (STA) in a wirelesslocal area network (WLAN) system, the method comprising: receiving atrigger frame from the AP; based on receiving the trigger frame, settingtwo bits of an uplink Physical layer Protocol Data Unit (PPDU) to anacknowledgement (ACK) policy value, wherein the two bits are arranged inan ACK policy subfield in a Quality of Service (QoS) control field ofthe uplink PPDU; and transmitting the uplink PPDU to the AP in theuplink multi-user transmission scheme, wherein the ACK policy value forthe uplink PPDU is selected, by the STA, from among a first set ofallowable ACK policy values for the uplink multi-user transmissionscheme, wherein the first set of allowable ACK policy values comprises afirst ACK policy value representing a ‘normal ACK’ or ‘an implicit blockACK request,’ and a second ACK policy value representing a ‘no ACK’,wherein the first set of allowable ACK policy values excludes a thirdACK policy value representing ‘Block ACK’, wherein based on a downlinkPPDU being received in a downlink multi-user transmission scheme fromthe AP, the ACK policy value for the downlink PPDU is selected, by theAP, from a second set of allowable ACK policy values for the downlinkmulti-user transmission scheme, wherein the second set of allowable ACKpolicy values comprises the first ACK policy value, the second ACKpolicy value, and the third ACK policy value, and wherein a use of thefirst set of allowable ACK policy values and the second set of allowableACK policy values is based on whether the uplink multi-user transmissionscheme is used or the downlink multi-user transmission scheme is used.2. The method according to claim 1, wherein the STA sets the ACK policyvalue for the uplink PPDU transmitted based on the trigger frame to thefirst ACK policy value.
 3. The method according to claim 2, furthercomprising, after transmission of the uplink PPDU with the ACK policyvalue set to the first ACK policy value, receiving an ACK/NACK signalfor the uplink PPDU from the AP.
 4. The method according to claim 3,wherein the ACK/NACK signal is received a short inter-frame space (SIFS)after the transmission of the uplink PPDU with the ACK policy value setto the first ACK policy value.
 5. A station (STA) configured to accessan access point (AP) in an uplink multi-user transmission scheme in awireless local area network (WLAN) system, the STA comprising: at leastone transceiver; at least one processor; and at least one computermemory operably connected to the processor and storing instructionsthat, based on being executed by the at least one processor, performoperations comprising: receiving, via the at least one transceiver; atrigger frame from the AP; based on receiving the trigger frame, settingtwo bits of an uplink Physical layer Protocol Data Unit (PPDU) to anacknowledgement (ACK) policy value, wherein the two bits are arranged inan ACK policy subfield in a Quality of Service (QoS) control field ofthe uplink PPDU; and transmitting, via the at least one transceiver, theuplink PPDU to the AP in the uplink multi-user transmission scheme,wherein the ACK policy value for the uplink PPDU is selected, by theSTA, from among a first set of allowable ACK policy values for theuplink multi-user transmission scheme, wherein the first set ofallowable ACK policy values comprises a first ACK policy valuerepresenting a ‘normal ACK’ or ‘an implicit block ACK request,’ and asecond ACK policy value representing a ‘no ACK’, wherein the first setof allowable ACK policy values excludes a third ACK policy valuerepresenting ‘Block ACK’, wherein based on a downlink PPDU beingreceived in a downlink multi-user transmission scheme from the AP, theACK policy value for the downlink PPDU received from the AP is fromamong, from a second set of allowable ACK policy values for the downlinkmulti-user transmission scheme, wherein the second set of allowable ACKpolicy values comprises the first ACK policy value, the second ACKpolicy value, and the third ACK policy value, and wherein a use of thefirst set of allowable ACK policy values and the second set of allowableACK policy values is based on whether the uplink multi-user transmissionscheme is used or the downlink multi-user transmission scheme is used.6. The STA according to claim 5, wherein the operations furthercomprise: setting the ACK policy value for the uplink PPDU transmittedbased on the trigger frame to the first ACK policy value.
 7. A methodfor receiving uplink Physical layer Protocol Data Units (PPDUs) from aplurality of stations (STAs) in an uplink multi-user transmission schemeby an access point (AP) in a wireless local area network (WLAN) system,the method comprising: transmitting a trigger frame to the plurality ofSTAs; and receiving an uplink PPDU from the plurality of STAs in theuplink multi-user transmission scheme, wherein two bits of the uplinkPPDU are set to an acknowledgement (ACK) policy value, wherein the twobits are arranged in an ACK policy subfield in a Quality of Service(QoS) control field of the uplink PPDU, wherein the ACK policy value forthe uplink PPDU is selected, by the plurality of STAs, from among afirst set of allowable ACK policy values for the uplink multi-usertransmission scheme, wherein the first set of allowable ACK policyvalues comprises a first ACK policy value representing a ‘normal ACK’ or‘an implicit block ACK request,’ and a second ACK policy valuerepresenting a ‘no ACK’, wherein the first set of allowable ACK policyvalues excludes a third ACK policy value representing ‘Block ACK’,wherein based on a downlink PPDU being transmitted from the AP in adownlink multi-user transmission scheme from the AP, the ACK policyvalue for the downlink PPDU is selected, by the AP, from a second set ofallowable ACK policy values for the downlink multi-user transmissionscheme, wherein the second set of allowable ACK policy values comprisesthe first ACK policy value, the second ACK policy value, and the thirdACK policy value, and wherein a use of the first set of allowable ACKpolicy values and the second set of allowable ACK policy values is basedon whether the uplink multi-user transmission scheme is used or thedownlink multi-user transmission scheme is used.
 8. The method accordingto claim 7, wherein the ACK policy value for the uplink PPDU receivedbased on the trigger frame is set to the first ACK policy value.
 9. Anaccess point (AP) configured to receive uplink Physical layer ProtocolData Units (PPDUs) from a plurality of stations (STAs) in an uplinkmulti-user transmission scheme in a wireless local area network (WLAN)system, the AP comprising: at least one transceiver; at least oneprocessor; and at least one computer memory operably connected to theprocessor and storing instructions that, based on being executed by theat least one processor, perform operations comprising: transmitting atrigger frame to the plurality of STAs; and receiving an uplink PPDUfrom the plurality of STAs in the uplink multi-user transmission scheme,wherein two bits of the uplink PPDU are set to an acknowledgement (ACK)policy value, wherein the two bits are arranged in an ACK policysubfield in a Quality of Service (QoS) control field of the uplink PPDU,wherein the ACK policy value for the uplink PPDU received from theplurality of STAs is from among a first set of allowable ACK policyvalues for the uplink multi-user transmission scheme, wherein the firstset of allowable ACK policy values comprises a first ACK policy valuerepresenting a ‘normal ACK’ or ‘an implicit block ACK request,’ and asecond ACK policy value representing a ‘no ACK’, wherein the first setof allowable ACK policy values excludes a third ACK policy valuerepresenting ‘Block ACK’, wherein based on a downlink PPDU beingtransmitted from the AP in a downlink multi-user transmission schemefrom the AP, the ACK policy value for the downlink PPDU is selected, bythe AP, from a second set of allowable ACK policy values for thedownlink multi-user transmission scheme, wherein the second set ofallowable ACK policy values comprises the first ACK policy value, thesecond ACK policy value, and the third ACK policy value, and wherein ause of the first set of allowable ACK policy values and the second setof allowable ACK policy values is based on whether the uplink multi-usertransmission scheme is used or the downlink multi-user transmissionscheme is used.
 10. The AP according to claim 9, wherein the ACK policyvalue for the uplink PPDU received based on the trigger frame is set tothe first ACK policy value.